In a manufacturing process of a semiconductor device using a photolithography technique, etching is used to be performed on a silicon oxide film (SiO2 film) used as, e.g., an insulation film and the like. For example, in a parallel plate type processing apparatus, the etching on the silicon oxide film is performed by ionizing an etching gas in a plasma atmosphere to allow the ionized etching gas to chemically react with the silicon oxide film.
In general, a fluorocarbon-based gas whose chemical formula is expressed by CxFy (x, y represent natural numbers) has been used as an etching gas for etching the silicon oxide film. Conventionally, a low-order saturated fluorocarbon-based gas such as CF4 and C4F8 having a small number of carbon atoms is used to be employed. Recently, however, an unsaturated fluorocarbon-based gas such as C4F6 begins to be used as the etching gas (see, for example, Japanese Patent Laid-open Application No. H6-275568). Since the unsaturated etching gas is difficult to be decomposed and easy to be polymerized in comparison with the conventional one, it would be deposited on a mask surface of the silicon oxide film as a protection film to thereby provide a high etching selectivity.
In case of using the unsaturated etching gas such as C4F6, however, the ratio of fluorine atoms to carbon atoms is decreased and at the same time, the absolute amount of the fluorine atoms gets reduced compared with the case of using the saturated gas such as CF4, resulting in a reduction of an etching rate. Since single sheet type etching apparatuses have been most commonly employed in recent days, the reduction of the etching rate would result in a significant decrease in productivity of semiconductor devices.